On the market there are two different types of outer covering for disposable diapers and sanitary towels, the first type consists of a matt polyethylene film, 18-22 microns thick, the second is obtained by lamination or co-extrusion of a 10-22 micron thick polyethylene film with an unwoven polypropylene fabric to give it a more textile appearance.
Both Types may be breathable or non-breathable.
Breathable films have a water vapour permeable micro-porous structure that is impermeable to liquid water by capillary pressure. U.S. Pat. No. 6,682,775 by Imerys describes that this structure is obtained by loading a polymer with an important percentage of mineral particles treated superficially with a waterproofing substance that is non adhesive to the base polymer, then extruding the compound as a film by any of the known technologies and subjecting it to single or bi-directional stretching of 1.2-2.5 times in order to increase the size of the pores and join them together.
The non-breathable films are obtained by extrusion and micro embossing of low-density polyethylene, generally linear using titanium dioxide pigments to obtain the desired whiteness and opacity.
Depending on the type of machinery used to make the diapers, and more specifically of the tensions the film is subject to in its passage through this machinery, more or less thickness of the film is necessary to guarantee its dimensional stability. Thus, older machines use films of up to 22 microns and more modern machines use around 18 microns thickness.
Our patent intends to obtain a micro-porous structure with pores of smaller size than in breathable films and not joined to each other, hence not breathable, so a significant reduction of density is achieved at the same time as thanks to the fact that they maintain good mechanical properties at low tensions, they can be manufactured in less thickness, maintaining enhanced dimensional stability in the machines making diapers.